With the constant growth of the bandwidth demand, the optical communication network achieves a huge application advantage from the transmission field to the access field. Because of the broad distribution of the optical communication network, a large number of optical communication modules are used inevitably. To further reduce the optical module cost in the network, the industry proposed using the PLC technology to replace the conventional free-space optical module. FIG. 1 shows a main structure of a typical PLC optical module. Generally, as same with the free-space optical module, a single PLC optical module structure needs to include a sending unit (LD) and a receiving unit (PD), and the difference lies in that optical signals are transmitted through a waveguide. The optical module sends light (solid arrow) or receives light (dotted arrow) to the communication network through a network interface, where light of two different wavelengths is used. Because of existence of the light of different wavelengths, a WDM component is required to make the distinction. Generally, the WDM component may reflect light of a certain band, and transmit light of another band.
In the structure of the PLC optical module shown in FIG. 1, because coupling efficiency between a laser and waveguide is limited, a part of light may spread out of the waveguide in a form of stray light. This part of light enters the receiver, and will have an adverse impact on performance of the receiver and cause crosstalk, thereby leading to deterioration of the performance of the entire optical module.